A magnetron rotary cathode sputtering apparatus has a magnetic field-generating device on the inside of a cylindrical sputtering target and is designed to carry out sputtering while cooling from the inside of the target and rotating the target, and the entire surface of the target material undergoes erosion and is uniformly shaved off, whereby it is possible to obtain a remarkably high target utilization ratio (at least 60%) as compared with the utilization ratio (from 20 to 30%) of a conventional planar magnetron sputtering apparatus. Further, by rotating the target, it is possible to input a large power per unit area as compared with a conventional planar magnetron sputtering apparatus, whereby a high film deposition rate can be obtained (see Patent Document 1).
As the process for producing a ceramic target used in a magnetron rotary cathode sputtering apparatus, there have known, e.g. a process for forming a target layer on an outer peripheral side of an cylindrical base material by a plasma spray method (see Patent Document 2), and a process for filling powder in an outer peripheral side of an cylindrical base material, and forming and bonding a target by a hot isostatic press (HIP) (see Patent Document 3).
However, an arc spray method and an HIP method not only require an expensive apparatus to carry out these methods and a large operating cost, but also are uneconomical since a cylindrical base material is made integrally with a cylindrical target material, making it difficult to reuse the cylindrical base material. Further, these methods are likely to be subjected to peeling or cracking attributable to the difference in the thermal expansion coefficient between both materials.
As the process for producing a ceramic target at a low cost, it has been strongly desired to develop a process for bonding a separately produced cylindrical target material made of a ceramic sintered body by means of a bonding material, such as a solder material. Such a desired process has advantages of, e.g. being capable of obtaining a quality film and a high production yield since a ceramic sintered body having a high density is usable in comparison with an arc spray method and an HIP method. As the process for producing a cylindrical ceramic sputtering target by means of a solder material, there has been known a process for sealing one end of each of a cylindrical target material and a cylindrical base material and introducing the cylindrical base material into the cylindrical target material with a solder material in a molten state being put therein (see Patent Document 4).
However, this method has caused a decrease in volume attributable to a phase change of the solder material from a liquid state to a solid state, and a decrease in volume attributable to cooling from the melting point of the solder material to normal temperature, whereby the occurrence of bonding layer defect attributable to such a decrease in volume has made thermal conduction poor, has caused a crack and a chip, or has generated extraordinary discharge due to poor electrical conduction in some cases. Further, this method has produced a needle-like protrusion called a nodule during sputtering, whereby extraordinary discharge is generated or particles are produced in some cases. For example, in a case where the solder material is made of generally used In, the volume decreases by 2.7% when the solder material is solidified at 156.6° C., the volume decreases by 1.2% when the solder material is cooled from 156.6° C. to 25° C., and the volume finally decreases by 3.9%. It should be noted that such a cylindrical ceramic target material generally has a smaller thermal expansion coefficient than a cylindrical base material. For this reason, when a bonding material is cooled from its melting point to normal temperature, the volume of a cavity defined by a cylindrical ceramic target material and a cylindrical base material is increased to causes bonding defects beyond expectation based on such a decrease in volume of the above-mentioned solder material made of In. These phenomena are not problematic in a conventional planar sputtering target since even if the volume of the bonding material is deceased, the distance between the planar target material and the planar base material is made narrower accordingly. These phenomena have a problem inherent to a cylindrical sputtering target because of being caused only in such a cylindrical sputtering target. Such a cylindrical sputtering target has been liable to cause a problem of a crack, a chip, extraordinary discharge and a nodule attributable to bonding layer defect since a larger power per unit area is input as compared with such a planar sputtering target.
As a method for inspecting the bonded state of a ceramic material or a metal material when such a material is bonded by means of a bonding material, there has been known a method for applying an X-ray to one side of an object to be measured, detecting a transmitted X-ray on the other side and determining the presence and absence of a bonding material based on a difference in X-ray absorption in respective parts of the object to be measured. No review has been made on whether the above-mentioned problem inherent to a cylindrical sputtering target, i.e. the occurrence of a crack, a chip, extraordinary discharge and a nodule is relevant to the state of a bonding layer in the cylindrical sputtering target, which is assumed not to be identified by the other methods.